FOUR-STROKE INTERNAL COMBUSTION ENGINE

MOTEUR A COMBUSTION INTERNE A QUATRE TEMPS

English Abstract

A four-stroke internal combustion engine (20) is provided. There is provided
within an engine housing (28) an oil reservoir (126) and
a valve chamber (156) which independently communicate with a crank chamber
(124). A strategically placed divider (116) and passageway,
located within the engine housing (28), appropriately direct lubricant within
the engine housing (28) so that the internal cavity of the engine
is lubricated during use in various operating attitudes, and so that the fluid
flows to and is held in the proper chambers of the engine
housing during storage. There is also provided a breather arrangement for an
internal combustion engine (20) which includes a cam shaft
(98) having a hollow passageway in communication with the crank chamber (124)
and the air intake system of the engine. There is also
provided an engine housing which can be utilized for engines having different
horse power ratings. There is also provided a crankshaft
bearing assembly (68, 70) which prevents damage to the bearing upon insertion
of the crankshaft (80) into the crank chamber (124).

French Abstract

l'invention concerne un moteur (20) à combustion interne à quatre temps. Ce moteur comprend un bloc moteur (28) un carter d'huile (126) et un logement de soupapes (156) qui communique de façon indépendante avec un carter du moteur (124). Une chicane (116 ) stratégiquement placée et un passage, situés dans le corps de moteur (28), canalisent de façon appropriée l'huile de graissage dans le corps de moteur (28) de sorte que la cavité intérieure du moteur est lubrifiée dans diverses positions, et de sorte qu'elle s'écoule et soit retenue dans les chambres du corps du moteur appropriées pendant l'arrêt. L'invention concerne aussi un reniflard pour moteur (20) à combustion interne qui comprend un arbre à cames (98) possédant un passage creux en liaison avec le carter du moteur (124) et avec le système d'admission du moteur. L'invention concerne encore un bloc moteur qui peut être utilisé pour des moteurs de puissances différentes. Enfin, l'invention concerne un ensemble palier de vilebrequin (68, 70) qui ne risque pas d'être endommagé lors de l'insertion du vilebrequin (80) dans le carter du moteur.

Claims

32

CLAIMS

1. A four-stroke internal combustion engine,
comprising:
an engine housing including a crankcase and a
cylinder;
an intake valve and exhaust valve disposed within
the engine housing;
a crank chamber disposed within said crankcase;
a crankshaft supported for rotation within said
crank chamber;
a piston operably interconnected with said
crankshaft for reciprocation within said cylinder in
response to rotation of said crankshaft;
an oil reservoir disposed within said crankcase,
and in fluid flow communication with said crank chamber;
a curved divider at least partially separating
said crank chamber from said oil reservoir, wherein the
curved divider is substantially U-shaped; and
a piston bore extension extending at least
partially into said crank chamber to define a lubricant
receiving space between said divider and said piston bore
extension.

2. An engine as set forth in claim 1, wherein said
divider includes an opening, such that said crank chamber
and said oil reservoir are in fluid flow communication
through said opening.





33

3. An engine as set forth in claim 2, wherein said
divider further includes a second opening and a third
opening, said second opening positioned substantially across
from said third opening, said crank chamber and said oil
reservoir being in fluid flow communication through said
second and third openings.

4. An engine as set forth in claim 1, wherein one
side of the divider is exposed to the oil reservoir and an
opposite side of the divider is exposed to the crank
chamber.

5. A four-stroke internal combustion engine,
comprising:
an engine housing including a crankcase and a
cylinder;
an intake valve and exhaust valve disposed within
the engine housing;
a crank chamber disposed within said crankcase;
a crankshaft supported for rotation within said
cram: chamber;
a piston operably interconnected with said
crankshaft for reciprocation within said cylinder in
response to rotation of said crankshaft;
an oil reservoir disposed within said crankcase,
and in fluid flow communication with said crank chamber;
a curved divider at least partially separating
said crank chamber from said oil reservoir; and
a piston bore extension extending at least
partially into said crank chamber to define a lubricant



34


receiving space between said divider and said piston bore
extension,
wherein said divider includes an opening, such
that said crank chamber and said oil reservoir are in fluid
flow communication through said opening,
wherein said divider further includes a second
opening and a third opening, said second opening positioned
substantially across from said third opening, said crank
chamber and said oil reservoir being in fluid flow
communication through said second and third openings.

6. An engine as set forth in claim 5, wherein the
curved divider is substantially U-shaped.

7. An engine as set forth in claim 6, wherein one
side of the divider is exposed to the oil reservoir and an
opposite side of the divider is exposed to the crank
chamber.

8. A four-stroke internal combustion engine,
comprising:
an engine housing including a crankcase and a
cylinder;
an intake valve and exhaust valve disposed within
the engine housing;
a crank chamber disposed within said crankcase;
a crankshaft supported for rotation within said
crank chamber;
a piston operably interconnected with said
crankshaft for reciprocation within said cylinder in
response to rotation of said crankshaft;


35


an oil reservoir disposed within said crankcase,
and in fluid flow communication with said crank chamber;
a divider at least partially separating said crank
chamber from said oil reservoir, wherein said divider
includes first and second openings, said first opening
positioned substantially across from said second opening,
said crank chamber and said oil reservoir being in fluid
flow communication through said first and second openings.

9. An engine as set forth in claim 8, further
comprising a piston bore extension extending at least
partially into said crank chamber to define a lubricant
receiving space between said divider and said piston bore
extension.

10. An engine as set forth in claim 8, wherein said
divider includes a third opening positioned between the first
and second openings on the divider wall such that said crank
chamber and said oil reservoir are in fluid flow
communication through said first, second, and third openings.

11. An engine as set forth in claim 8, wherein the
divider is substantially U-shaped.

12. An engine as set forth in claim 11, wherein one
side of the divider is exposed to the oil reservoir and an
opposite side of the divider is exposed to the crank
chamber.

Description

CA 02368207 2004-02-18
67363-1214
:l_
FOUR-STROKE INTERNAL COMBUSTION ENGINE
FIELD OF THE 1NVENTION
The present invention relates, generally, to four-stroke internal combustion
engines
and, more particularly, to four-stroke internal combustion engines used in
trimmers,
blowers, vacuums, chain saws, other hand-held power tools, snowblowers,
generators,
vegetation cutting devices such as lawn mowers, or other outdoor power
equipment.:
BACKGROUND OF THE INYENTTON
Many hand-held power tools or other outdoor power equipment are powered by
electric motors or two-stroke internal combustion engines. Electric motors are
limited to
certain applications due to the available power for products utilizing a cord,
and battery
longevity for cordless products. Conventional two-stroke engines include a
lubricating
means in which the lubricant is mixed with fuel which allows the engines to
operate in any
given position such as upright, inclined, sideways or upside down. For
example, when .
using a chain saw, the chain saw is typically capable of use in either an
upright, sideways
or upside down condition. Over the past few years, there has been a
requirement by
various governing bodies to reduce the emissions associated with all~siriall
gas engines,
particularly, conventional two-stroke engines. Thus, because four-stioke
engines do not
require the mixing of lubricant and fuel, it is desirable to use four-stroke
engines in place
of conventional two-stroke engines, since four-stroke engines normally release
fewer
undesirable emissions as compared to the amount of undesirable emissions
released by
conventional two-stroke engines. .



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-2-
However, previously, it was widely viewed that four-stroke internal combustion
engines could only be used for limited applications, such as lawn mowers,
snowblowers,
generators, or other portable products having wheels. It was thought that
these prior four-
stroke engines were too heavy and cumbersome to be used in operator-carned
power tools.
Moreover, since it is generally necessary to store oil separate from the gas
so that the oil
can be used for lubrication, traditional low-cost four-stroke engines were not
designed to
operate in any position other than a substantially upright position because if
the engine
was significantly tipped or tilted, the lubricant would foul the engine. Only
very recently
has it been contemplated that a four-stroke engine may be used in a hand-held
power tool
or in other applications where the engine may operate in a tipped or tilted
condition.
SUMMARY OF THE INVENTION
Accordingly, there is a need for a four-stroke internal combustion engine that
is
capable of use in various power tools, and yet is also capable of having low
emissions and
being sufficiently light to be carried by an operator when desired. What is
also needed is a
four-stroke internal combustion engine that is capable of operating in many
different
attitudes of the engine. What is also needed is a four-stroke engine that
eliminates the
need for an elaborate lubrication system. What is needed is a four-stroke
internal
combustion engine which accomplishes these features and other features and
which is also
economical to manufacture.
In one embodiment of the present invention, there is provided a four-stroke
internal
combustion engine, preferably a side valve or "L" head engine, having an
engine housing
which includes a crankcase and a cylinder. A cylinder head which at least
partially defines
a combustion chamber is positioned adjacent to the cylinder. An intake valve
and an
exhaust valve are disposed within the engine housing. A crank chamber and an
oil
reservoir are disposed within the crankcase in such a way that the oil
reservoir is in fluid
flow communication with the crank chamber. A strategically placed agitator,
located at
least partially within the crank chamber, moves lubricant within the engine
housing during
operation of the engine to lubricate the necessary components of the engine.
A divider is disposed within the crankcase to at least partially divide the
crank
chamber and the oil reservoir. The divider assists in directing the lubricant
during
operation and storage of the engine in order to prevent a substantial amount
of lubricant



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-3-
from undesirably migrating into the combustion chamber when the engine is
operated or
stored in an upright or tilted position. In one aspect of the present
invention, the divider
defines a path which extends about the divider. The path allows lubricant in
the oil
reservoir to flow around a substantial portion of the divider to further
enhance the
lubricating and storage features of the engine according to the principles of
the present
invention.
The engine is constructed of light weight material and appropriately sized so
that
the engine is sufficiently light enough to be usable in hand-held power tools.
Thus, the
four-stroke internal combustion engine according to the present invention may
be utilized
in those applications which are traditionally limited to the use of two-stroke
internal
combustion engines.
In one aspect of the present invention, the divider includes at least one
opening
such that the crank chamber and the oil reservoir are in fluid flow
communication through
the opening. The opening helps ensure that the crank chamber is substantially
continuously lubricated during operation of the engine, even if the engine is
operated
under a tilted condition. The opening in the divider is positioned such that
at least some of
the lubricant found in the crank chamber after operation of the engine may
flow back into
the oil reservoir even if the engine is stored in a tilted state. Preferably,
the divider
includes a plurality of openings.
In another aspect of the present invention, the engine housing further
includes a
cylinder side wall which at least partially extends into the crank chamber to
define a
lubricant receiving space between the divider and the cylinder side wall.
Preferably, the
cylinder side wall at least partially defines a piston bore. During operation,
as the agitator
mixes and slings lubricant around the inside cavity of the engine as a result
of the rotating
action of the agitator, the lubricant is more likely to be slung into the open
area between
the divider and the cylinder side wall rather than into the piston bore.
Moreover, during
storage, the open area or lubricant receiving space provides additional space
for the
lubricant to be held if the engine is stored in a sideways or upside down
position to also
prevent a substantial amount of the lubricant from flowing into the piston
bore. As
previously noted, migration of the lubricant into the combustion chamber leads
to an
unwanted condition. A function of the lubricant receiving space is to inhibit
lubricant
from reaching the piston bore, thereby preventing a substantial amount of
lubricant from
reaching the combustion chamber.



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
_4_
In another aspect of the present invention, the engine housing further
includes a
valve chamber. The intake valve and exhaust valve are disposed within the
valve chamber
and the valve chamber is in fluid flow communication with the crank chamber.
The
operation of the agitator, the pressure pulses created within the engine
during operation of
the engine, the communication of the oil reservoir with the crank chamber, and
the
communication of the crank chamber with the valve chamber together allow the
working
components found within the valve chamber to be lubricated, even if the engine
is
operated in a tilted manner. Preferably, the valve chamber is also in fluid
flow
communication with the cylinder side wall to further enhance the lubrication
of the
working components located within the valve chamber. The strategic positioning
of the
fluid flow openings into the valve chamber will prevent the valve chamber from
receiving
too large of a quantity of lubricant when the engine is being operated or
being stored.
In another embodiment of the present invention, the engine includes a
cantilevered
crankshaft which has opposite ends and which is substantially located within
the crank
chamber. The agitator includes a counterweight which is interconnected to the
cantilevered end of the crankshaft. The counterweight is adapted to reduce
windage
resistance on the crankshaft and to sling lubricant about the crank chamber as
the
crankshaft rotates during operation of the engine. Further, the counterweight
throws the
lubricant away from the main bearings of the crankshaft, thereby substantially
preventing
the main bearings from being flooded by the lubricant during operation of the
engine. The
divider may be provided with a scraper which is used to limit the amount of
lubricant
which comes into contact with the agitator or the counterweight. The scraper
preferably at
least partially extends into the crank chamber, so that as the agitator
rotates past the
scraper during operation of the engine, the scraper meters the amount of
lubricant which
comes into contact with the agitator.
In another aspect of the present invention, a cam shaft disposed substantially
normal to the crankshaft is rotatably driven by the crankshaft. The
substantially normal
arrangement of the cam shaft and crankshaft enables the engine to be longer in
a direction
parallel to a power take off, as compared to a conventional engine in which
the cam shaft
is parallel with the crankshaft. Such an engine is desirable in certain hand-
held power tool
applications, such as power trimmers, in order to provide an overall better
balance of the
power tool for the convenience of the user. The substantially normal
arrangement of the
shafts also allows for an intake port and an exhaust port disposed in the
cylinder to be



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-5-
significantly spaced apart. Segregating the ports will reduce heat migration
from the
exhaust port to the intake port which could result in hot restart (e.g., vapor
lock) problems.
Preferably, the intake and exhaust ports are elliptical in shape. The
elliptical
configuration of the ports enables the overall profile or height of the engine
housing to be
reduced, thereby reducing the amount of material needed for the overall engine
housing.
This helps reduce the overall weight of the engine housing. The port walls are
provided
with sufficient surface area and strength to support the portion of the engine
housing and
cylinder head disposed above the ports. The substantially normal relationship
between the
crankshaft and the cam shaft also allows the valves to be disposed
substantially normal to
the crankshaft. A first valve tappet associated with the intake valve and a
second valve
tappet associated with the exhaust valve operatively engage the cam shaft to
provide for
the proper operation of the valves with respect to a four-stroke internal
combustion engine.
Such a compact arrangement further limits the overall weight of the engine.
In another embodiment of the present invention, a breather arrangement for the
four-stroke internal combustion engine is provided. The cam shaft is provided
with an
axial passageway and several radial apertures. The radial apertures
communicate with the
crank chamber and the passageway. A breather tube communicates with the
passageway
and an air intake system of the engine. A check-valve is positioned between
the end of the
cam shaft and the air intake system to maintain the negative pressure created
within the
engine. Blow-by gas inside the engine is admitted into the radial aperture of
the cam shaft
and is sent through the axial passageway of the cam shaft and into the
breather tube, so
that the blow-by gas is recirculated within the engine. The pressure pulses
created within
the engine cause the blow-by gas to enter the cam shaft and be recirculated as
described.
However, the centrifugal action of the cam shaft counters the action created
by the
pressure pulses, thereby substantially preventing the heavier lubricant, as
compared to the
blow-by gas, from entering the radial apertures in the cam shaft. As a result,
the lubricant
will substantially remain within the cavity of the engine and will not travel
through the
breather tube to the air intake system of the engine.
In another aspect of the present invention, the engine housing is designed to
cooperate with a piston found within the piston bore such that a connecting
rod can be
conveniently attached to the piston and the crankshaft. The crankcase and the
piston each
include an access hole. A connecting rod is operatively attached to the
crankshaft and the
piston in the following manner. The access hole in the crankcase and the
access hole or



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-6-
aperture in the piston are aligned during installation of a wrist pin. The
wrist pin is
inserted into the piston aperture and through an end of the connecting rod to
connect the
connecting rod to the piston. A star washer is used to hold the wrist pin in
place after
installation.
The compact size of the engine according to the present invention and the
cantilevered crankshaft make it difficult to assemble the internal components
of the
engine, such as the piston-connecting rod-crankshaft assembly. The cooperation
of the
access holes in the crankcase and the piston allow for easy assembly of the
piston-
connecting rod-crankshaft assembly. Preferably, it is desirable to use the
same engine
housing casting for engines having different horsepower ratings, simply by
changing the
connecting rod and thus, the length of the piston throw. To facilitate
assembly and to
permit the same engine housing casting to be used for different sized engines,
an elliptical,
or the like, wrist pin boss is formed in the crankcase of the engine housing.
The wrist pin
boss can be machined at its upper end to provide an access hole in the
crankcase for a first
horsepower rating or piston throw, and the wrist pin boss can be machined at
its lower end
to provide an access hole in the crankcase for a second horsepower rating or
piston throw.
After the wrist pin boss is properly machined, the wrist pin-which connects
the piston to
the connecting rod-is inserted through the crankcase aperture and into the
piston aperture
as previously explained. In this way, the same engine housing casting can be
used for
different sized engines.
In another aspect of the present invention, the crank chamber includes at
least two
bearing pockets. One of the pockets has a larger diameter than the other. Both
of the
bearing pockets are disposed on the same side of the internal cylinder side
wall. The
cantilevered crankshaft is supported by two main bearings located in the
respective
bearing pockets. The bearing pocket nearest the cantilevered (input) end of
the crankshaft
is the larger diameter bearing pocket so that the bearing pockets can be
machined in the
crank chamber from the same side with a single tool thereby eliminating
unnecessary
tooling requirements. This provides a significant savings in capital costs and
manufacturing expenses. Preferably, before assembling the crankshaft in the
crank
chamber, the outer bearing and then the agitator or counterweight are properly
positioned
around the cantilevered end of the crankshaft. The counterweight is provided
with an
access aperture in order to allow a tool to appropriately contact the adjacent
bearing and



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
_'7_
the crankshaft. In this way, as the crankshaft is placed into the crank
chamber, the bearing
is not damaged and the crankshaft is properly positioned.
In another aspect of the present invention, the combustion chamber is adapted
to
enhance swirl of the air/fuel mixture to increase efficiency of the engine.
Preferably, a
spark plug is positioned closer to the exhaust valve than the intake valve to
also improve
engine efficiency, and reduce the likelihood of self ignition within the
engine.
In another aspect of the present invention, the engine housing is designed in
such a
way so as to permit two engine housings to be produced using only one die tool
and one
die casting machine. This also reduces capital costs and manufacturing
expenses.
In another aspect of the present invention, a starter assembly is attached to
the rear
of the engine and is designed to utilize a crankshaft pin which is integral
with the
crankshaft. The crankshaft pin is the contact point for the internal rotation
of the
crankshaft in order to start the engine.
In another aspect of the present invention, the blower housing has an inwardly
extending hub. The hub fits over the crankshaft. The starter assembly slides
onto the hub.
A star washer or the like is placed over the hub so as to prevent the axial
movement of the
starter assembly, particularly the pulley. This arrangement eliminates the
need for
separate mounting bosses and fasteners which are normally needed to attach the
starter
assembly to the blower housing and which typically block the cooling air flow
by the fan.
In another aspect of the present invention, a shroud is provided to at least
partially
surround the engine housing. The shroud is provided with a pair of opposed
channels. A
fuel tank having opposed, outwardly extending shoulders is held by the shroud
as the
shoulders are received by the respective channels. Preferably, a filler
material is
positioned between each of the channels and respective shoulders so as to
provide a more
snug fit between the shroud and the fuel tank.
In a preferred embodiment, a fuel line includes a fuel filter attached to the
end of
the fuel line disposed within the fuel tank. The fuel filter acts as a weight.
During
operation of the engine, as the engine is tipped in different orientations,
the weighted fuel
line swings to the bottom of the fuel tank so that fuel is always picked up by
the fuel line
regardless of the orientation of the engine.
In one aspect of the present invention, the shroud includes an opening around
the
intake port. An intake isolator is provided having an air/fuel passageway
extending
therethrough. The intake isolator is mounted to the engine housing so that the
air/fuel



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
_g_
passageway of the intake isolator is aligned with the intake port. Further,
the intake
isolator is positioned within the opening of the shroud to substantially
ensure that cooling
air passing between the engine housing and the shroud cannot escape through
the opening
in the shroud. The intake isolator is also used to insulate the intake
air/fuel mixture from
the surrounding environment to the extent feasible to ensure that the air/fuel
ratio remains
substantially correctly calibrated. In one embodiment of the present
invention, a
carburetor is interconnected with the intake isolator.
In one aspect of the present invention, the shroud includes a plurality of
raised
portions on one side thereof. If desired, the engine can be placed on the
ground to rest on
the raised portions. This could be useful, for example, on a trimmer when the
user desires
to change the cutting line located on the end of the shaft which is spaced a
significant
distance from the engine.
In another aspect of the present invention, the engine housing includes a back
plate
which is adjacent to a flywheel. Preferably, the crankcase, the cylinder and
the back plate
are cast as a single component, thereby reducing manufacturing and assembly
costs, and
thereby limiting the overall size of the engine housing. In a preferred
embodiment, the
engine housing further includes at least one fin integrally formed thereto.
The fin extends
from the back plate and beneath the crankcase to increase the stability
between the back
plate and the crankcase. The fin also is adapted to help cool the engine
housing,
particularly, the crankcase.
In another aspect of the present invention, a muffler is connected to the
engine
housing. The muffler includes a boss which extends into the exhaust port. In
one
embodiment, the engine housing includes an angled, stepped sealing surface
located in the
exhaust port. The end of the muffler boss mates against the exhaust port
sealing surface to
substantially prevent the exhaust from undesirably escaping into the
surrounding
atmosphere. Preferably, a sealing gasket is positioned between the end of the
boss and the
exhaust port sealing surface to even better prevent the exhaust from
undesirably escaping
into the atmosphere. In another embodiment, the muffler boss is surrounded by
a portion
of the exhaust port to define a clearance between the outside liner of the
boss and the
adjacent surface of the exhaust port. A gasket is positioned between the
muffler and the
engine housing to seal the clearance space between the muffler and the engine
housing so
as to prevent exhaust from undesirably escaping into the atmosphere. In a
preferred


CA 02368207 2004-02-18
67363-1214
-9-
embodiment, the gasket is an enlarged gasket which also serves as a heat
shield between
the engine housing and the user.
In one aspect of the present invention, the muffler includes a pair of outer
shells
having a pair of mounting bolt holes extending therethrough for receiving a
pair of
mounting bolts. A pair of bolt receiving bores are located on opposite sides
of the exhaust
port in the engine housing. This arrangement ensures that the muffler will be
securely
attached to the engine housing in a stable manner. In a preferred embodiment,
the muffler
includes an inner shell sandwiched between the outer shells. The inner shell
is a baffle
plate adapted to reduce the amount of exhaust admitted into the atmosphere.
The inner
shell also includes a pair of mounting bolt holes to receive the mounting
bolts. In yet
another preferred embodiment, one of the outer shells includes a shoulder
extending
around an edge of the outer shell. The other outer shell includes a hook-
shaped flange
extending around an edge of the outer shell. The hook-shaped flange of the one
outer shell
receives the shoulder of the other outer shell upon assembly of the muffler.
The assembly
1$ is such that if exhaust leaks out of the muffler, the exhaust will leak
away fi~om the engine
housing so as not to substantially heat the engine housing.
In one aspect of the present invention, the four-stroke internal combustion
engine
includes an engine housing having an integrally formed crankcase, cylinder and
flywheel
back plate. The flywheel back plate includes at least one mounting boss on one
side and at
least one other mounting boss on an opposite side. An assembly fixture is
utilized to hold
the engine housing during assembly of the engine. Each mounting boss on the
flywheel
back plate receives a separate pin of the assembly fixture to secure the
engine housing to
the assembly fixture: A shroud is provided to at least partially surround the
engine
housing. The shroud includes at least two slots such that the slots surround
the pins of the
assembly fixture when the shroud is positioned around the engine. The shroud
can then be
firmly attached to the engine. After the shroud is attached to the engine, the
pins can be
removed from the mounting bosses. In this manner, the engine can be
substantially
completely assembled while the engine is mounted to the assembly fixture.


CA 02368207 2005-06-10
6736:3-1214
-9a-
In one aspect of the present invention, there is
provided a four-stroke internal combustion engine,
comprising: an engine housing including a crankcase and a
cylinder; an intake valve and exhaust valve disposed within
the engine housing; a crank chamber disposed within said
cranlscase; a crankshaft supported for rotation within said
cranlt chamber; a piston operably interconnected with said
cranlsshaft for reciprocation within said cylinder in response
to rotation of said crankshaft; an oil reservoir disposed
within said crankcase, and in fluid flow communication with
said crank chamber; a curved divider at least partially
separating said crank chamber from said oil reservoir,
wherein the curved divider is substantially U-shaped; and a
piston bore extension extending at least partially into said
crank chamber to define a lubricant receiving space between
said divider and said piston bore extension.
In one aspect of the present invention, there is
prow=ided a four-stroke internal combustion engine,
comprising: an engine housing including a crankcase and a
cylinder; an intake valve and exhaust valve disposed within
the Engine housing; a crank chamber disposed within said
cranlccase; a crankshaft supported for rotation within said
crank chamber; a piston operably interconnected with said
crankshaft for reciprocation within said cylinder in
response to rotation of said crankshaft; an oil reservoir
disposed within said crankcase, and in fluid flow
communication with said crank chamber; a curved divider at
leasi~ partially separating said crank chamber from said oil
reservoir; and a piston bore extension extending at least
partially into said crank chamber to define a lubricant
rece_Lving space between said divider and said piston bore
extension, wherein said divider includes an opening, such
that said crank chamber and said oil reservoir are in fluid


CA 02368207 2005-06-10
67363-1214
-9b-
flow communication through said opening, wherein said
divider further includes a second opening and a third
opening, said second opening positioned substantially across
from said third opening, said crank chamber and said oil
reservoir being in fluid flow communication through said
second and third openings.
In one aspect of the present invention, there is
provided a four-stroke internal combustion engine,
comprising: an engine housing including a crankcase and a
cylinder; an intake valve and exhaust valve disposed within
the engine housing; a crank chamber disposed within said
crankcase; a crankshaft supported for rotation within said
crank chamber; a piston operably interconnected with said
crankshaft for reciprocation within said cylinder in
response to rotation of said crankshaft; an oil reservoir
disposed within said crankcase, and in fluid flow
communication with said crank chamber; a divider at least
partially separating said crank chamber from said oil
reservoir, wherein said divider includes first and second
openings, said first opening positioned substantially across
from said second opening, said crank chamber and said oil
reservoir being in fluid flow communication through said
first: and second openings.
Accordingly, it is a principal feature of the
present invention to provide a four-stroke internal
combustion engine which includes a simple and inexpensive
lubricating system which enables the engine to be functional
in various operational attitudes.
It is a feature of the present invention to
provide a four-stroke engine incorporating the foregoing
features and yet also simple and easy to manufacture and
assemble.



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-10-
Other features and advantages of the invention will become apparent to those
skilled in the art upon review of the following detailed description, claims
and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded perspective view of a four-stroke internal combustion
engine
according to the present invention.
FIG. lA is a perspective view of the four-stroke engine of FIG. 1 illustrating
the
engine as assembled for use with, e.g., a power trimmer.
FIG. 2 is a cross-sectional end view and a partial schematic view of the
engine of
FIG. 1 taken along line 2-2 of FIG. 3.
FIG. 3 is a cross-sectional side view of the assembled engine of FIG. 1.
FIG. 4 is an enlarged view of a portion of the engine shown in FIG. 3
illustrating
the rotational relationship between a cam gear and a crank gear, a portion of
a lubricant
flow path, and a portion of a breather system for the engine shown in FIG. 1.
FIG. S is an enlarged view of a portion of the engine shown in FIG. 3
illustrating a
piston in its bottom dead center position.
FIG. 6 is a schematic representation illustrating another aspect of the
present
invention which concerns the attachment of a connecting rod to a piston and a
crankshaft.
FIG. 7 is a perspective front view taken along line 7-7 of FIG. 9 illustrating
a
counterweight positioned adjacent to a main bearing of the crankshaft.
FIG. 7A is a side view of the counterweight of FIG. 7.
FIG. 7B is another perspective view of the counterweight of FIG. 7.
FIG. 8 is a perspective view illustrating an agitator cooperating with a
scraper
found on a wall within the engine cavity in order to regulate the amount of
lubricant which
comes into contact with the agitator.
FIG. 8A shows the rotational movement of the agitator of FIG. 8 and how the
scraper controls the lubricant which comes into contact with the agitator.
FIG. 9 is a schematic representation of another aspect of the present
invention
illustrating the positioning of a crankshaft within a crank chamber disposed
in an engine
housing.
FIG. 10 is a partial schematic view of a top portion of the engine housing
taken
along line 10-10 of FIG. 3 illustrating the spatial relationship between a
combustion
chamber, a piston bore, an intake valve and an exhaust valve.



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-11-
FIG. 11 is a partial schematic view of a cylinder head taken along line 11-11
of
FIG. 3 illustrating the spatial relationship between the combustion chamber,
the piston
bore, the intake valve, the exhaust valve and portions of a spark plug.
FIG. 12 is a schematic view illustrating the path of an air/fuel mixture
through an
intake system to the combustion chamber and the path of the exhaust out of the
combustion chamber through an exhaust system in an engine according to the
present
invention.
FIG. 13 is a cross-sectional partial schematic view of an engine according to
the
present invention showing the state of the lubricant in the crank chamber and
an oil
reservoir when the engine is in an upside down state.
FIG. 14 is a cross-sectional view of another embodiment of the present
invention
showing a starter assembly attached to the rear of a four-stroke internal
combustion
engine.
FIGS. 15-18 are schematic representations of two engine housings which are
capable of being produced using one die tool and one die casting machine.
FIG. 19 is a schematic view of a power trimmer in which another four-stroke
internal combustion engine according to the present invention is employed.
FIG. 20 is a perspective view of a shroud which at least partially surrounds
an
engine, wherein the shroud is adapted to enhance overall assembly operations
of the
engine.
FIG. 21 is an exploded partial perspective view of the four-stroke engine of
FIG.
19.
FIG. 22 is another exploded partial perspective view of the four-stroke engine
of
FIG. 19.
FIG. 23 is a perspective view of an engine housing with a muffler attached
thereto.
FIG. 24 is an exploded perspective view of FIG. 23.
FIG. 25 is a perspective view illustrating the flywheel end of the engine
housing of
FIG. 23.
FIG. 26 is an enlarged partial cross-sectional view taken along line 26-26 of
FIG.
23 illustrating a connection between the engine housing and muffler of FIG.
23.
FIG. 27 is an alternative connection between the engine housing and muffler of
FIG. 26.
FIG. 28 is a perspective view of the engine housing of FIG. 23 without the
muffler.



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-12-
FIG. 29 is a front view of an intake isolator as shown in FIG. 22 and FIG. 20.
FIG. 30 is a cross-sectional view of the intake isolator of FIG. 29.
FIG. 31 is a partial cross-sectional side view of the assembled engine of
FIGS. 21
and 22.
FIG. 32 is an enlarged view of a portion of the engine shown in FIG. 31
illustrating
a piston in its bottom dead center position.
FIG. 33 is an enlarged view of the relationship between the shroud and starter
assembly in terms of retaining the starter assembly on the shroud.
FIGS. 34-38 illustrate various views of the starter pulley shown in FIG. 33.
FIGS. 39-40 are schematic representations of two engine housings which are
capable of being produced using one die tool and one die casting machine.
Before the embodiments of the invention are explained in detail, it is to be
understood that the invention is not limited in its application to the details
of construction
and the arrangements of components set forth in the following description or
illustrated in
the drawings. The invention is capable of other embodiments and of being
practiced or of
being carried out in various ways. Also, it is to be understood that the
phraseology and
terminology used herein is for the purpose of description and should not be
regarded as
limiting.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Illustrated in FIG. lA of the drawings is a four-stroke internal combustion
engine
20 according to the present invention. The engine 20 drives a conventional
shaft typically
housed in a shaft tube 22 which in turn drives an implement having a rotary
head, cutting
filament or blade, rotary impeller, or the like, depending on the type of
power tool in use
(see, e.g., FIG. 19). The shaft arrangement shown in FIG. lA (and FIG. 19),
typically
used in conjunction with a hand-held power trimmer, is used for illustrative
purposes only
and it should be understood that other power tools such as those mentioned
previously
herein are capable of utilizing the four-stroke engine of the present
invention. In other
words, generally, the engine according to the present invention is preferably
used in an
orientation where the implement or working tool has an axis which is
substantially parallel
with a crankshaft axis. The engine according to the present invention may also
be
orientated with the crankshaft being horizontal or vertical. The engine
according to the
present invention is particularly well suited for those applications in which
high RPMs,



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-13-
e.g., 3,000 RPMs up to 7,000-8,000 RPMs or more, may be required and in which
an
output of less than 1 to over 6 horsepower may be supplied. Importantly,
whichever type
of power tool is used in combination with the four-stroke engine according to
the present
invention, the engine is capable of working, at least temporarily, in
substantially any
operational position of the power tool.
Illustrated in FIG. 1 of the drawings is an exploded perspective view showing
various components of the four-stroke internal combustion engine 20 according
to the
present invention. Shown in FIG. 1 is a side valve or "L" head engine in which
the
various features of the present invention are employed. Side valve engines are
sometimes
referred to as "L" head engines because of the positional relationship of an
intake valve
and an exhaust valve with respect to a combustion chamber. As will be apparent
below,
the "L" is in reference to the path taken by an air/fuel mixture and the
exhaust through
respective valves and ports found in the engine body. Also, importantly, in an
"L" head
engine, the intake valve port and the exhaust valve port are located in the
engine housing,
not in the cylinder head which is generally common to overhead valve or
overhead cam
engines.
Before describing in detail the various features of the present invention, the
components shown in FIG. 1 are identified for the sake of clarity. Shown are
an ignition
coil screw 24 used to attach an ignition coil (not shown) to the engine 20;
shroud screws
27 attach shroud 26 to an engine housing 28; cover screws 30 attach sump cover
32 and
sump cover gasket 34 to the engine housing 28 in order to seal one end of the
engine
housing 28; cylinder head screws 36 attach cylinder head 38 and cylinder head
gasket 40
to the engine housing 28 thereby at least partially defining a combustion
chamber 39 (FIG.
2); carburetor 42 and muffler 44 are appropriately connected to the engine 20;
carburetor
42 cooperates with intake port 41 and air cleaner or filter 43 (FIG. 2);
muffler 44
cooperates with exhaust port 45; flywheel 46 which includes an integral fan
(not shown) is
positioned between the shroud 26 and engine housing 28 with the help of a
flywheel key
(not shown) in order to cool the engine 20 during operation; piston 48 is
received by piston
bore 50 within engine housing 28; intake valve 52 and exhaust valve 54 are
positioned
adjacent piston bore SO within engine housing 28; intake valve seat 56 and
exhaust valve
seat 58 are placed within engine housing 28 to cooperate with the respective
heads of
valves 52 and 54; valve springs 60 are placed in a valve spring chamber and
held within
the valve spring chamber by valve spring keepers 62; the valve spring chamber
is sealed



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-14-
by valve cover 64 and valve cover gasket 66; crankshaft bearing 68, crankshaft
bearing 70,
worm-helical or spiral gear 74, counterweight 76, crank pin 78 and crankshaft
80 are part
of crankshaft assembly 82; counterweight 76 includes an aperture 77;
connecting rod 84
includes connecting rod bearings 86 and 88; one end of connecting rod 84 fits
over crank
pin 78 and a wrist pin 90 connects the other end of connecting rod 84 to
piston 48 by
sliding in aperture 92 of piston 48; wrist pin 90 cooperates with access hole
93 of engine
housing 28 when attaching the connecting rod 84 to the piston 48; cam shaft
bushing 94,
cam shaft bushing 96, cam shaft 98, cam lobes 100 and 102 (FIG. 2), and worm-
helical or
spiral gear 104 are part of cam shaft assembly 106; cam cap 108 and cam cap
gasket 110
are attached to engine housing 28 by cam cap screws 111 in order to seal cam
shaft
assembly 106; tappets 112 are properly positioned within the engine 20 to
cooperate with
valves 52 and 54; spark plug 114 is positioned in a spark plug hole within
cylinder head
38; divider 116 having slots 118, 120 and 122 is disposed within engine
housing 28 and at
least partially defines a crank chamber 124 and a lubricant or oil reservoir
126; and the
piston bore 50 includes an extension 128 which at least partially extends into
crank
chamber 124.
Other components and features not clearly shown in FIG. 1 will be described
below according to the features of the present invention.
FIG. 1 shows the carburetor 42 and the exhaust muffler 44 mounted on opposite
sides of the engine housing 28. The carburetor 42 may be of any type of
carburetor that is
tippable such as a standard variable venturi diaphragm carburetor found in
small gas
engines, but a rotary valve carburetor available from, e.g., Walbro, is
particularly well
suited for use in an engine according to the present invention. The air
cleaner or filter 43
(schematically shown in FIG. 2) is mounted in or near an inlet of an intake
passage in the
carburetor 42. A fuel tank (not shown in FIG. 1) is mounted typically to a
lower surface of
the engine housing 28 and cooperates with the carburetor 42 so that fuel and
air can be
supplied to the intake port 41 (FIG. 2) in the engine housing.
The engine housing 28 is typically made of a lightweight aluminum alloy
casting
having a cylindrical bore or piston bore 50 formed therein. As noted, the
piston bore 50 is
configured to partially extend into the crank chamber 124 disposed within the
engine
housing 28. The area or space 136 (FIG. 13) between the extended piston bore
50 and
divider 116 accepts volumes of the lubricant or oil during operation and
storage to prevent
too much lubricant or oil from entering the piston bore SO or valve chamber
156 (FIG. 2).



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-15-
The piston 48 is preferably coated, such as with an iron coating, or chrome
plated so as to
eliminate the need for a sleeve such as an iron sleeve within the piston bore
50.
Alternatively, piston bore 50 may include an iron cylinder sleeve.
The divider preferably includes bottom slot 118 which is located directly
below the
piston bore S0. Optional side slots 120 and 122 of the divider 116 may be
located
substantially directly across from one another at a predetermined distance
from the bottom
of the piston bore 50. The slots 118, 120 and 122 may be replaced with one or
more holes
or other apertures. As noted, the present invention is, of course, not limited
to a
particularly sized engine, but may be used with any internal combustion
engine. The
design considerations to determine the size and location of the slots or holes
will be
apparent below. The slots or holes should be configured for different sized
engines taking
into consideration the various features of the present invention.
FIGS. 8 and 8A show another aspect of the divider 116. In operation, as shown,
the counterweight 76 is caused to rotate in one direction, usually, a
clockwise direction.
The bottom slot 118 includes opposing sides 130 and 132. The second side 132,
with
respect to the direction of travel of the counterweight 76, has a scraper 134
adjacent
thereto. Preferably, the scraper 134 is positioned within .020 to .060 inches
of the
counterweight 76 when the counterweight 76 is located closest to the scraper
134. The
scraper 134 limits or meters the amount of lubricant or oil (shown in broken
dotted lines)
which comes into direct contact with the counterweight 76. The scraper 134
helps to limit
the amount of lubricant or oil which may be slung into the piston bore 50
during operation
and reduces the wind resistance caused by excessive lubricant on counterweight
76. It
should be noted that the scraper 134 could be configured in other ways. For
example,
bottom slot 118 in the divider 116 could be a diagonal slot such that the
second side of the
diagonal slot acts as the scraper 134 but the scraper is not a raised scraper
as shown in
FIGS. 8 and 8A. Alternatively, the bottom slot 118 in the divider 116 could be
a straight
slot without the use of a scraper.
As noted, FIG. 1 shows the oil reservoir 126 disposed within the engine
housing 28
defined by the divider 116 and the engine housing 28. The oil reservoir 126 is
in fluid
flow communication with the crank chamber 124, preferably through slots 118,
120 and
122. As shown, the oil reservoir 126 and the divider 116 are substantially
curved or U-
shaped. The divider 116 is preferably curved to direct lubricant away from the
piston bore
SO when the engine is tipped or inverted. The communication between the two
chambers



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-16-
124 and 126 allows for the crank chamber 124 to be properly lubricated during
use as the
lubricant is allowed to flow between the two chambers 124 and 126 during use,
and for the
lubricant to flow back into the oil reservoir 126 during storage so that an
excessive amount
of lubricant does not adversely flow into the piston bore 50.
Refernng to FIGS. 1 and 3, crankshaft 80 is mounted within the crank chamber
124. The crankshaft worm-helical or spiral gear 74 drives the cam shaft
assembly 106.
Worm-helical or spiral gears are commonly known in the art and readily
available from
any number of gear manufacturers and suppliers. The crankshaft 80 and gear 74
may be
manufactured in any number of known ways. However, injection molding the gear
around
a trim metal piece representing the crankshaft would work well according to
the principles
of the subject invention. The injection mold material may be a thermoplastic
material or
nylon material known to those skilled in the art. Another alternative is to
provide a metal
crankshaft with an enlarged cylindrical piece of metal on the crank where a
worm-helical
or spiral gear is intended to be located. The crankshaft then is subjected to
a bobbing
procedure in which the gear is machined on the crankshaft.
Still refernng to FIGS. 1 and 3, bearings 68 and 70 are positioned around the
crankshaft 80 in order to support the cantilevered crankshaft 80 when it is
placed within
the crank chamber 124. The bearings 68 and 70 are placed on opposite sides of
the worm-
helical or spiral gear 74 and on the same side of the piston bore 50. The
inner bearing 68
is smaller in diameter than the outer bearing 70. The bearings 68 and 70 are
dimensioned
in this manner such that the bearing pockets found in the crank chamber 124
are machined
from one side of the engine housing 28 using only one tool. As can be
appreciated by
those skilled in the art, machining bearing pockets from one direction reduces
equipment,
time and expense usually associated with having to machine bearing pockets
from
different directions.
As shown in FIG. 1, counterweight 76 is mounted on one end of the crankshaft
80.
FIGS. 7, 7A and 7B show in greater detail the shape and contours of the
counterweight 76.
As generally understood, the forces resulting from the operation of the piston
48, the
connecting rod 84 and the associated components, are balanced by the
counterweight 76.
Depending on the size of the engine, more than one counterweight may be
necessary. The
counterweight 76 includes wing-tipped aerodynamic sides 138 and 140. Each wing-
tipped
side includes a back 142 that is positioned adjacent the main bearing 70 and a
front 144
opposite the back 142. The wing-tipped sides 138 and 140 have contoured
surfaces that



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-17-
extend from the back 140 to the front 142 of the counterweight 76. In this
way, as will be
more evident below, the aerodynamic shape of the counterweight 76 assists in
reducing air
resistance on the counterweight 76, generating the proper turbulence of air
and lubricant
within the internal cavity of the engine 20 and directing the lubricant within
the internal
cavity of the engine 20.
The tool access hole or aperture 77 of counterweight 76 (FIG. 7) is used for
positioning the crankshaft 80 within the crank chamber 124. FIGS. 7 and 9
schematically
show a tool 146 which is used to position the outer bearing 70, counterweight
76 and the
crankshaft 80 within the crank chamber 124. Bearing 68 is press fitted into
the crank
chamber 124 and is adapted to receive one end of the crankshaft 80. Once the
crankshaft
80 has been manufactured, the bearing 70 is press fitted onto the crankshaft
80. The
counterweight 76 is then fixed to the crankshaft 80. FIG. 7A illustrates a
step 141 which
provides a clearance of approximately .050 of an inch between the
counterweight 76 and
bearing 70. As shown in FIG. 7, only portions 69 of the outside race of the
main bearing
70 are exposed after the counterweight 76 is placed on the crankshaft 80. The
access
aperture 77 allows the tool 146 (FIG. 9) to contact the outside race of the
main bearing 70
in three spots when assembling the crankshaft 80 and associated components of
the
crankshaft assembly 82 into the crank chamber 124. A fourth leg of the tool
(FIG. 9)
contacts the cantilevered end of the crankshaft 80. This assembly helps ensure
that the
main bearing 70 will not be damaged upon assembly and the crankshaft 80 will
be
properly seated when inserted into the crank chamber 124.
FIG. 6 schematically illustrates how the connecting rod 84 is attached to the
crankshaft 80 and piston 48. A custom shoulder bolt (not shown) may be
utilized to affix
the connecting rod 84 to the crank pin 78. The entire crankshaft assembly 82
(FIG. 1) is
mounted within the crank chamber 124 (FIG. 3). The piston 48 is slid into the
piston bore
50 from the top of the engine housing 28. The aperture 92 in the piston 48 is
lined up with
the access aperture 93 in the engine housing 28. The connecting rod 84 is
attached to the
crankshaft assembly 82 by virtue of crank pin 78 and positioned within a cut
out portion
148 of the piston 48. The wrist pin 90 is inserted through the access hole 93
of the engine
housing 28 into the access hole 92 of the piston 48 and through the bearing 86
of the
connecting rod 84. Since the aperture 92 of the piston 48 is not drilled all
the way through
the piston 48, one end of the wrist pin 90 abuts an inner portion 150 of the
piston 48. The
wrist pin 90 can be held in place within the piston 48 by a star washer 151
inserted in the



CA 02368207 2001-07-20
WO 00/43655 PCT/LTS00/00841
-18-
open end of the aperture 92 (see also FIG. 5). Preferably, the wrist pin 90
and the crank
pin 78 are hollow so as to reduce the overall weight of the reciprocating mass
which in
turn means a smaller counterweight with less weight is needed to balance the
forces
generated by the reciprocating mass. Reducing the overall weight of the
reciprocating
components improves vibration and makes the engine lighter for ease of
operation.
The cam shaft 98, the eccentric style cam lobes 100 and 102 and the cam gear
104
are shown as separate parts in FIG. 2. It should be noted that these parts can
be injected
molded as a single component using, for example, a thermoplastic or nylon
material.
Alternatively, certain components maybe injected molded around a piece of trim
metal to
create the final assembly in similar manner to that contemplated for the
crankshaft 80 and
worm-helical or spiral gear 74.
FIG. 2 illustrates that the cam shaft 98 includes a passageway 152. FIGS. 2, 3
and
4 show that a portion of the cam shaft assembly 106 (FIG. 1) adjacent the worm-
helical or
spiral gear 104 includes at least one radial aperture 154 exposed to the
passageway 152
and crank chamber 124. The passageway 152 and aperture 154 may be drilled into
the
proper portions of the cam shaft assembly 106 or molded therein. Essentially,
the
passageway 152 and the aperture 154 and cam shaft assembly 106 cooperate to
provide a
breather arrangement for the internal combustion engine which will be fully
outlined
below. Further, the radial aperture 154 may be found in a radial disc (not
shown) attached
to the cam shaft assembly 106 in close proximity to the gear 104 so as to be
in
communication with the passageway 152 and crank chamber 124.
As shown, the cam shaft 98 is located normal to the crankshaft 80. As can be
appreciated by those skilled in the art, generally, in typical small gas
engines, the cam
shaft and the crankshaft are parallel to one another, not normal as shown
according to the
present invention. A parallel arrangement leads to a wider engine whereas the
normal
arrangement according to the present invention leads to a longer engine design
with the
crankshaft axis being substantially parallel to the longitudinal axis of the
tool. A longer
unit is particularly desirable for those hand-held applications such as power
trimmers
which require better balance for ease of operation. A wider engine may tend to
cause the
unit to want to rotate in the operator's hands during use.
FIG. 2 shows that cam shaft 98 sits in bushings 94 and 96 which rest in
respective
pockets within the crank chamber 124 in engine housing 28. The worm-helical or
spiral
gears 74 and 104 (FIGS. 2 and 3) are preferably designed such that when cam
shaft 98 is



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-19-
placed generally normal to crankshaft 80, the gears 74 and 104 mesh so that
the rotational
relationship between the crankshaft 80 to cam shaft 98 is 2 to 1.
The tappets 112 and the intake valve 52 and the exhaust valve 54 cooperate
with
cam shaft 98 (FIG. 2). Intake valve 52 and exhaust valve 54 are positioned
within engine
housing 28 adjacent to piston 48 and piston bore 50. The valves 52 and 54 are
positioned
such that the valve heads are closer to the centerline of the bore 50 as
compared to the
lower portions of the valves (FIG. 3). Preferably, the valves 52 and 54 are
set at an angle
of approximately between zero and eight degrees from a line parallel with the
centerline of
the bore. The intake valve seat 56 and the exhaust valve seat 58 are placed
within engine
housing 28 and cooperate with the heads of the respective valves 52 and 54 to
alternately
create a seal or an opening into the combustion chamber 39 with respect to the
ports 41
and 45. The valve spring keepers 62 and valve compression springs 60 are
positioned
within the valve chamber 156 (FIG. 2). Each tappet 112 includes a respective
head 158
which is in operational contact with respective cam lobes 100 and 102. As the
cam shaft
98 rotates by virtue of drive gear 74, cam lobes 100 and 102 properly engage
tappets 112
such that valves 52 and 54 move up and down as is commonly understood by those
skilled
in the art.
With reference to FIGS. 2, 3 and 4, the crank chamber 124 is in communication
with the valve chamber 156 via access passageway or aperture 160.
Additionally, the
valve chamber 156 is in communication with the piston bore 50 via access
passageway or
aperture 162. The passageways 160 and 162 allow valve chamber 156 and the
components therein to receive lubricant during operation of the engine 20 in
substantially
any attitude. Additionally, during storage, with the aid of divider 116, the
extended piston
bore S0, and the slots 118, 120 and 122, a significant amount of lubricant
will not remain
or flow into the valve chamber 156.
Refernng to FIGS. l, 2 and 3, cylinder head gasket 40 is positioned between
the
cylinder head 38 and the engine housing 28 so as to provide a proper seal
between the two.
Spark plug 114 projects into the enclosed combustion chamber 39. Spark plug
114 fires in
combination with the ignition coil and magneto (not shown) to provide the
necessary
charge or high voltage signal to ignite the air/fuel mixture in the combustion
chamber 39
when the engine 20 is in operational mode.
FIGS. 10 and 11 schematically show, at least in part, the combustion chamber
39
with respect to the intake valve 52, exhaust valve 54 and piston bore 50. As
shown, the



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-20-
combustion chamber 39 only partially extends over the piston bore 50. The
orientation of
the combustion chamber 39 and shape of the combustion chamber 39 enhances
swirl in the
mixing chamber 39 so as to provide a better air/fuel mixture to enhance
ignition of the
mixture. Also, the spark plug 114 is positioned closer to the exhaust valve 54
than it is to
the intake valve 52. The electrode 164 is properly oriented to provide a
firing spark.
Placing the spark plug 114 nearer the exhaust valve 54 allows the hotter
air/fuel mixture to
be burned sooner by the spark ignited flame front. This will reduce the self
ignition
tendency of the hotter air/fuel mixture at the exhaust side of the combustion
chamber 39.
If the spark plug 114 is positioned closer to the intake valve 52, there is a
risk of having
two combustions, resulting in a loss of power.
As shown in FIG. 2, the intake port 41 and the exhaust port 45 are located 180
degrees apart from each other. The position of the valves 52 and 54 is a
result of the
substantially normal arrangement of the cam shaft 98 and crankshaft 80 and
allows the
ports 41 and 45 to be positioned on opposite sides of the engine housing 28.
This provides
an additional feature of operator safety. For example, when using a power
trimmer, the
exhaust port 45 and muffler 44 (FIG. 1) are positioned farther away from the
operator
during use. Another advantage of placing the ports 41 and 45 as far apart as
possible is to
reduce heat migration from the exhaust port 45 to the intake port 41 which, if
did occur,
could result in hot restart vapor lock issues, or difficulty in calibrating
the air/fuel ratio.
FIG. 12, with reference to FIGS. 2 and 10 as needed, shows a schematic
representation of the path traveled by the air/fuel mixture and exhaust
through the engine
20. The air/fuel mixture enters the intake port 41, travels past the intake
valve 52, and into
the combustion chamber 39. The engine 20 combusts the air/fuel mixture in
order to
generate power, and the remaining exhaust travels past the exhaust valve 54
and out the
exhaust port 45. The arrangement of the cam shaft 98 and the crankshaft 80 is
also shown
to illustrate how such an arrangement contributes to the overall scheme
associated with the
air/fuel and exhaust paths through the engine 20.
An important feature of the present invention is that the four-stroke engine
according to the present invention is capable of use in substantially any
position. A
problem with prior conventional four-stroke engines is that if the engine is
substantially
tilted, the lubricant will run into undesirable locations, such as the
carburetor, thereby
causing the engine to malfunction or cease working altogether. The four-stroke
engine



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-21-
according to the present invention is designed to solve this problem and other
problems
typically associated with conventional four-stroke engines.
The oil or lubricant reservoir 126, the crank chamber 124, the piston bore 50,
and
the valve chamber 156 include strategically placed slots, passageways, or
apertures so as
S to enable various working components within the engine to be lubricated at
virtually all
times during operation. Additionally, in cooperation with the divider 116, the
counterweight 76 has been designed such that only a proper amount of lubricant
comes
into contact with the counterweight 76. The design of the counterweight 76
also allows
the counterweight to meter the amount of lubricant that finds its way to the
main bearing
70 so as not to flood that part of the crank chamber 124 encapsulating the
gears 74 and
104. This also will help prevent too much lubricant from entering the valve
chamber 156
through passageway 160 and 162. Moreover, the piston bore SO and divider 116
have
been designed to ensure that the lubricant has a place to go regardless of
whether the
engine is operating or being stored, so as not to foul the internal components
of the engine.
The piston bore 50, connecting rod 84, the crankshaft assembly 82, the cam
shaft
assembly 106, and the valve chamber 156 and the components therein all require
some
lubrication. It is a feature of the present invention to use a minimal amount
of lubricant or
oil to lubricate the engine. This is accomplished in a number of ways. First,
the highest
part that needs lubrication, considering when the engine is in an upright
(spark plug up)
condition, is the valve chamber 156. Second, the roller bearings 86 and 88 for
the
connecting rod 84 require less lubrication versus a solid shaft with aluminum
bushings.
Third, since the lubricant will follow the path of least resistance, the
divider 116, the
counterweight 76 and the various slots, apertures and passageways previously
mentioned
help direct the lubricant to particular areas of the engine depending on the
attitude of the
engine.
In an upright non-operating position, lubricant or oil is stored within the
oil or
lubricant reservoir 126. In this position and in this state, the level of the
lubricant is
preferably below the bottom slot 118 in the divider 116. During operation, the
reciprocating movement of the piston 48 creates pressure pulses within the
internal cavity
of the engine 20. The lubricant moves in response to the movement of the
piston 48. The
counterweight 76 agitates the lubricant or oil and blow-by gas within the
inside cavity of
the engine 20. As the piston 48 travels in its downward direction during the
intake and
power strokes, the lubricant is forced through the main bearing 70 to
lubricate the bearings



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-22-
70 and 68, the worm-helical or spiral gears 74 and 104, the crankshaft 80, the
cam shaft 98
and the bushings 94 and 96 due to increased pressure in the engine cavity. The
action of
the cam gear 104 will cause some lubricant to enter aperture 160 and migrate
to the valve
chamber 156. Moreover, any oil found in piston bore 50 could be pushed into
aperture
162 to also lubricate the valve chamber 156. On the upward strokes, i.e., the
compression
and exhaust strokes, the lubricant will be drawn back over the just mentioned
areas to
further lubricate the components due to a partial vacuum in the engine cavity.
The
reciprocating movement of the piston 48 moves the lubricant back and forth
within the
internal cavity of the engine 20. The invention does not require a control
valve to control
movement of the lubricant.
There are at least a couple of aspects to consider when discussing lubricating
the
engine 20. First, there is resistance or energy lost as the counterweight 76
agitates the
lubricant and blow-by gas. Second, it is undesirable to supply too much
lubricant to the
piston bore 50 and the valve chamber 156 which, if did occur, could result in
damage to
the engine 20.
As noted, since the static oil level is preferably below the bottom slot 118
in an
upright condition, the counterweight 76 preferably does not dip directly into
the lubricant,
although direct dipping could be used. The more direct contact made with the
lubrication,
the more energy that is lost from the engine 20. The least amount of lubricant
resistance is
desired. As mentioned, the counterweight 76 is designed to throw the lubricant
away from
the main bearing 70 and towards the sump cover 32. The design of the
counterweight 76
also limits the amount of lubricant slung into the piston bore 50. In this
way, only a limited
amount of oil will find its way to the valve chamber 156. The counterweight 76
is
designed to reduce the amount of drag that the counterweight 76 has when it is
rotating
through and churning up the lubricant. In addition, the counterweight 76
design reduces
windage which creates a more efficient engine. It should be noted that
although the
counterweight 76 is shown and described as the device which agitates the
lubricant and
blow-by gas within the internal cavity, a separate agitator may be provided to
accomplish
the same results. Such an agitator may be a splasher or mixer attached to the
rotating
crankshaft or connecting rod, or caused to rotate in any number of other ways.
In an upside down (spark plug down) position such as that shown in FIG. 13,
the
extended piston bore 50, the divider 116, the slots 118, 120 and 122, and the
passageways
160 and 162 (FIGS. 2 and 3) ensure that the engine will continue to function
properly, for



CA 02368207 2001-07-20
WO 00!43655 PCT/US00/00841
-23-
at least a, limited amount of time, or be capable of storage in this position
without fouling
the engine. During operation, the changing pressure pulses, the blow-by gas
and the
agitator 76 will cause the lubricant to be mixed and moved inside the cavity
of the engine
20. Although some oil will be flung into the piston bore 50, not a significant
amount will
go there. Also, it should be noted that the access passageway 162 is located
such that the
oil ring 166 in the piston 48 does not travel over or past the passageway 162
as the piston
48 reciprocates within the piston bore 50 (FIG.S). Otherwise, it would be
possible for
lubricant found within the valve chamber 156 to find its way into the
combustion chamber
39, thereby burning off the lubricant and creating excess emissions.
The crank chamber 124 includes the area or space 136 between the extended
piston
bore 50 and divider 116 for receiving oil or lubricant when the engine is
tilted or inverted
as representatively shown in FIG. 13. During storage, the slots 118, 120 and
122 will
allow most of the oil to remain in the oil reservoir 126, and the area 136
between the
divider 116 and the piston bore 50 will hold most of the remaining lubricant.
Any oil left
in the valve spring chamber 156 during use is thought to be negligible and
will not
significantly affect the operation of the motor. Importantly, because of the
positioning of
the slots 120 and 122 above the oil in the inverted position, the valve
chamber 156 will not
be able to receive any significant amount of oil.
To further explain certain features of the present invention, the oil
reservoir 126
should be in communication with the crank chamber 124 so as to allow for
proper
lubrication of the engine 20 in substantially any operational position. The
various
described slots, passageways, holes and apertures perform at least two
functions. First, if
the engine 20 is operating in a sideways condition, the slot 120 or 122 in the
divider wall
116 facing down towards the ground allows oil to travel into the crank chamber
124 with
the pressure pulsations in a manner similar to when the engine is in an
upright state during
which lubricant moves through the bottom slot 118. Second, if for whatever
reason, a
significant amount of lubricant finds its way to the crank chamber 124 during
operation
and the engine 20 is turned off and turned upside down or sideways for
storage, the side
slots 120 and 122 allow oil to migrate from the crank chamber 124 to the oil
reservoir 126
so as to prevent the piston bore 50 and valve chamber 126 from undesirably
receiving a
significant amount of lubricant.
Another important feature of the present invention is to be able to vent blow-
by gas
from the crank chamber 124 by separating the blow-by gas from the
lubricant/blow-by gas



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-24-
mixture. As described, the cam shaft 98 is provided with a hollow passageway
152 and
properly positioned radial passages 154. With reference to FIG. 2, one end of
the cam
shaft cover 108 includes a nipple 168 which is attached to a flexible hose 170
(schematically shown). Although not shown, there may be an oil seal placed
between the
cam cover 108 and engine housing 28. As the pressure pulse forces the
lubricant/blow-by
gas mixture through the main bearing 70, the blow-by gas is driven into the
radial holes
154 and passageway 152 while the oil is prevented from passing through the
holes 154 as
a result of the centrifugal action of the operating cam shaft 98. The blow-by
gas travels
through the cam cover 108 and nipple 168 affixed to cam cover 108, through the
flexible
hose 170 and back into the intake of the carburetor 42. A check valve may be
positioned
between the end of the cam shaft 98 and the air intake system to maintain the
negative
pressure created within the engine.
FIG. 14 shows a cross-sectional view of the four-stroke engine according to
the
present invention with a starter mechanism 172 attached to the sump cover
plate 32 with
screws 30. A crankshaft adapter 174 is connected to crank pin 78. A clutch
bearing 176 is
press fitted around the crankshaft adapter 174. A starter shaft 178 is
positioned around the
clutch bearing 176 and is keyed or molded to the starter 180. An oil seal or O-
ring 181 is
placed around the starter shaft 178 to provide a seal between the starter
mechanism 172
and the sump cover 32. A thrust washer or bearing 182 is placed on each side
of the
starter 180. Starter 180 is preferably a rewind starter having a pull cord
184. Locating the
starter mechanism 172 or the sump cover 32 on the back of the engine 20
enables the
operator to have easy access to the pull cord. Further, integrally connecting
the starter to
the piston 48 through connecting rod 84 and the crankshaft 80 through the
crank pin 78
reduces the rope pull force needed to start the engine 20. Alternatively,
other starter
assemblies may be utilized.
FIGS. 15-18 depict a layout for the dies used to manufacture an engine housing
according to the present invention. The engine housing is designed to permit
two engine
housings to be produced using one die tool and one die casting machine. The
engine
housing is designed to include walls which allow for the needed draft angles
given
different orientations for each engine housing within the die tool. The draft
angles enable
the engine housing to readily separate from the die. The engine housing is
designed to
permit slide tooling access (i.e., the piston and cam shaft bores) when two
engine housings
are fabricated from one tool. In FIGS. 15-18, the dies 188 and 190 are formed
so that the



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-25-
centerlines of the engine cylinder bores (which are parallel to direction C)
are parallel to
each other. Boxes 194 and 196 represent the edges of the tool. By positioning
the dies in
this manner, the inserts used to form the dies are inserted only along a few
directions, i.e.,
in directions A, B and C. This die configuration reduces the overall space
required to
make the engine housings, while still enabling two engine housings to be made
at the same
time. The two die halves 188 and 190 are parted along parting line 192. It
should be
noted that the back wall of the engine housing is not shown and is separately
formed and
then fastened to the engine housing with bolts or other suitable fasteners. It
is, however,
possible that the back wall could be formed integral with the engine housing
according to
the principles set forth above. It should also be noted that the parting line
192 could be
moved to another location. The draft angles of the engine housing outer walls
would
change accordingly so as to accommodate the new location of the parting line.
FIGS. 39-40 depict another embodiment of a layout for the die 529 used to
manufacture an engine housing according to the present invention. In this
embodiment, it
is still possible to permit two engine housings to be produced using one die
tool and one
die casting machine. The die 529 is laid out in such a manner that the
centerlines of the
piston bores are parallel but in opposite directions. Further, both cavities
are oriented such
that the stationary bodies of material compose the internal features of the
oil reservoir, the
barner wall and the inner crank chamber. The engine housing is designed to
include walls
of which are needed for draft angles parting line jumps, and slide shut-offs
for the given
orientation within the die layout. By orienting the die in such a prescribed
manner, the
inserts for the die pieces are inserted only along a few directions, i.e., in
directions D, E, F
and G. This embodiment of the die layout also serves to minimize the overall
space
necessary to manufacture the two-engine housings out of a single die.
With such a die layout, the datum targets or reference features for both
cavities are
created by the same piece of stationary material. By having these references
on the same
piece of stationary material, there is less variance to accommodate between
the casting in
the machining of the finished engine housing. This further translates into
less variance in
the finished-machined engine housing even though the casting is being derived
from two
separate cavities.
As shown, this embodiment also integrally creates the flywheel back-plate into
the
engine housing casting. It is further desirable to gate 531 the casting into
the deck of the
cylinder and route the gates parallel to directions F and G into the cavities.



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-26-
The engine 20 shown in FIG. 1 has been described in such a manner to identify
the
various aspects of the present invention. However, the features of the present
invention
described above may be incorporated into other four-stroke internal combustion
engine
configurations. Moreover, the features identified above may be slightly
modified to
accommodate different engine designs. As such, FIGS. 19-40 illustrate another
four-
stroke internal combustion engine in which the features previously described
may be
employed and which incorporates additional inventive features not yet
previously
described. It should be noted that the features specifically described in
relation to FIGS.
19-40 may be incorporated into the engine described in FIGS. 1-18, or other
engines.
FIG. 19 illustrates a four-stroke internal combustion engine 300 according to
the
present invention. The engine 300 is shown as used in a power trimmer but may
be used
in other devices as described for the engine of FIG. 1.
Again, before describing in detail the various features of the present
invention, the
components shown in FIGS. 21 and 22 are identified for the sake of clarity.
Many of the
components are assembled in the same or similar manner as described in
reference to FIG.
1 or as generally understood by those skilled in the art. Accordingly, the
manner of
assembly is not described in great detail below except if the manner of
assembly pertains
to specific features of the present invention. Greater detail of such features
will be
provided in reference to the drawings to follow when needed. Shown in FIG. 21
are spark
plug 302; cylinder head screws 304; cylinder 306; cylinder head gasket 308;
compression
rings 310 and 312 and oil ring 313 which are appropriately positioned in
annular slots
located in piston 314; connecting rod 316 and connecting rod bearings,
preferably needle
roller bearings, 318 and 320; exhaust valve 322, intake valve 324, valve
springs 326 and
valve spring keepers 328; engine housing 330; valve cover 332 and associated
screws 334;
flywheel 336, crankshaft adapter 338, ignition coil 340, wiring assemblies 342
and 346,
and screws 344 all of which are part of a starter assembly; muffler mounting
bolts 350;
muffler 352; and blower housing 348 which is part of an overall shroud further
described
below.
Shown in FIG. 22 are sealing O-ring 366 and oil gauge 367; intake gasket 368,
intake isolator 369 and screws 370; carburetor gasket 372, carburetor 374 and
O-ring 376;
air filter assembly 378, screws 380 and air filter cover 382; .wrist pin 384
and star washer
wrist pin retainer 386; oil sealing ring 388, roller bearing 390, crankshaft
392 and
counterweight 393; sump cover 394 and screws 396; muffler housing 398 which is
part of



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
_2~_
an overall shroud further described below and mounting screws 400; tappets
402, cam
shaft 404, cam shaft cover 406; screws 408 and breather tube 410; check valve
411; fuel
tank 412 having fuel line 414, opposing shoulders 416; and filter material 418
which is
placed around shoulders 416 as further described below.
Other components and features not clearly shown in FIGS. 21 and 22 will be
described below. Moreover, the significance of any of the components shown in
FIGS. 21
and 22 or their interaction, will be described below in conjunction with the
principles of
the present invention.
FIG. 23 more clearly shows the engine housing 330 with the muffler 352
attached
thereto by mounting bolts 350. The engine housing 330 includes a crankcase 420
and a
cylinder 422. The cylinder head 306 (FIG. 21), which at least partially
defines a
combustion chamber, is disposed adjacent to the cylinder 422. A crank chamber
426 is
disposed within the crankcase 420. An oil reservoir 428 is also disposed
within the
crankcase 420 and is in fluid flow communication with the crank chamber 426,
preferably,
through slot 430 and opposing holes 432 (only one being shown) disposed in a
divider
433. The divider 433 is disposed within the crankcase 420 and at least
partially divides the
crank chamber 426 and the oil reservoir 428. A plurality of holes 434 are
provided in the
engine housing 330 so that the sump cover 394 and sump cover gasket can be
attached
thereto. The engine housing 330 also includes an oversized wrist pin boss 436.
The wrist
pin boss 436 may be integrally formed with the divider 433. The function of
the wrist pin
boss 436 will be further described below. The engine housing 330 also includes
a
flywheel back plate 438 with at least one mounting boss 440, the function of
which will be
described below.
FIG. 24 is an exploded perspective view of FIG. 23 showing how the muffler 352
is connected to the engine housing 330. The cylinder 422 includes an exhaust
port 442
and an intake port 444 (FIG. 25). Preferably, the intake port 444 and exhaust
port 442 are
elliptical in shape thereby enabling the overall height of the engine housing
330 to be
reduced. This will naturally reduce the overall weight of the engine housing,
which is an
especially important factor for hand-held power tools. The walls of the ports
442 and 444
are provided with sufficient material so as to be able to support the weight
of the engine
housing 330 and cylinder head 306 disposed thereabove.
The muffler 352 includes a boss 446 which is preferably elliptical. The boss
446
extends into the exhaust port 442. Mounting bolts 350 extend through holes 448
in the



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
_28_
muffler 352 and into holes 450 formed in the cylinder 422. Preferably, the
holes 448 are
spaced apart and positioned on opposite sides of the exhaust port 442 to
maximize the
stability of the muffler 352 with respect to its connection to the cylinder
422.
FIGS. 26 and 27 are enlarged partial cross-sectional views taken along line 26-
26
S of FIG. 23 showing preferred alternative mounting connections between the
muffler 352
and cylinder 422. FIG. 26 shows the engine housing 330 having an angled, step
sealing
surface 452 located in the exhaust port 442 of cylinder 422. The end 454 of
boss 446 can
mate against the exhaust port sealing surface 452 to substantially prevent
exhaust from
undesirably escaping into the environment. Preferably, a sealing gasket 456 is
positioned
between the end 454 of the boss 446 and the sealing surface 452 to even better
prevent the
exhaust from escaping.
FIG. 27 shows the outside liner of the boss 446 of the muffler 352 surrounded
by
the surface 458 of the exhaust port 442, thereby defining a clearance space
460
therebetween. Although surface 458 is shown as an angled surface, it may take
on other
1 S configurations so long as clearance space is provided between the muffler
352 and the
exhaust port 442. A gasket 462 is positioned between the muffler 352 and
cylinder 422 or
engine housing 330 to seal the clearance space 460, thereby preventing exhaust
from
escaping into the atmosphere. Preferably, the gasket 462 is an enlarged gasket
which also
serves as a heat shield between the engine housing 330 and the muffler 352.
The muffler 352 (FIG. 24) preferably includes a pair of outer shells 464 and
466
having respective mounting bolt holes 448 for the mounting bolts 350. An inner
shell or
baffle plate (not shown) is preferably located between the outer shells 464
and 466. The
inner shell also is adapted to allow the mounting bolts 350 to pass
therethrough. The
baffle plate is designed to reduce noise. Outer shell 464 includes a shoulder
470 which
extends around an edge of the outer shell 464. Outer shell 466 includes a
flange (not
shown) which extends around an edge of the outer shell 466. Upon assembly, the
shoulder
470 receives the flange such that if exhaust does leak out of muffler 352, the
exhaust will
leak away from the engine. Although not shown, a deflector may be placed over
the
exhaust holes 372 (FIG. 23) of the muffler 352 to protect the operator from
receiving a
direct blast of exhaust.
Given the nature of the four-stroke engine according to the principles of the
present
invention, it is desirable to provide an economical engine with features which
allow the
engine to be easily assembled. One feature is to use the same engine housing
330 for



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-29-
engines having different horsepower ratings, simply by changing the connecting
rod 316
(FIG. 21) and thus, the length of the piston throw. To accomplish this
feature, the
oversized wrist pin boss 436 (FIG. 23) is provided. The wrist pin boss 436 can
be
machined at its upper end 474 to provide an access hole (not shown) in the
crankcase 420
for a first piston throw, and the wrist pin boss 436 can be machined at its
lower end 476 to
provide an access hole (not shown) in the crankcase 420 for a second piston
throw. After
the wrist pin boss 436 is properly machined, the wrist pin 384 (FIG. 22) is
inserted through
the crankcase access hole and into the piston access hole to connect the
piston 314 (FIG.
21) to the connecting rod 316 (FIG. 21). Accordingly, the same engine housing
330 can
be used for different sized engines. FIG. 31 shows a completed assembly on
such engine.
FIG. 32 shows the piston 314 in its bottom most dead center position so that
the wrist pin
384 can be appropriately positioned within the engine.
FIG. 28 is an enlarged view of the engine housing 330 of FIG. 24 without the
muffler 352. As shown, the divider 433 defines a path 478 which extends
substantially
about the divider 433 and over the wrist pin boss 436. The path 478 allows
lubricant
found in the oil reservoir 428 to flow around a substantial portion of the
divider 433 to
further enhance the lubricating and storage features according to the
principles of the
present invention. The path 478 allows the amount of lubricant found on both
sides of the
divider 433 to equalize when the engine 300 is turned upside down. This
further inhibits a
substantial amount of the lubricant from migrating into the crank chamber 426.
Another feature which reduces assembly costs of the engine thereby reducing
the
overall cost of the engine relates to the manner of assembling a shroud to the
engine
housing. As noted with reference to FIG. 23, the flywheel back plate 438 is
provided with
at least one mounting boss 440. FIG. 25 is a perspective view of the engine
housing 330
of FIG. 23 only from a different perspective. As shown, the opposite side of
the flywheel
back plate 438 also includes at least one mounting boss 480. Upon assembling
the engine
300, an assembly fixture (not shown) is adapted to hold the engine 300. Each
mounting
boss 440 and 480 receives a separate pin (not shown) of the assembly fixture
to secure the
engine housing 330 to the assembly fixture. A shroud 482 (FIG. 20) is provided
to at least
partially surround the engine housing 330. Preferably, the shroud comprises
the blower
housing 348 (see also FIG. 21) and muffler housing 398 (see also FIG. 22).
Shroud 482
includes at least one slot 484. Each slot 484 is designed to surround a
respective pin of the
assembly fixture extending out of the mounting bosses 440 and 480 when the
shroud 482



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-30-
is positioned around the engine housing 330. The shroud 482 can be attached to
the
engine housing 330 by threading screws 486 (FIG. 20) into respective holes
such as hole
488 (FIG. 25) of the engine housing 330. Thus, the entire engine 300 can be
substantially
assembled while remaining attached to a single assembly fixture.
Another feature of the shroud 482 is that the muffler housing 398 preferably
includes a plurality of raised portions 490 (FIG. 31). Thus, if desired, the
engine 300 may
be placed on the ground to rest on the raised portions 490. It should be noted
that the
blower housing 492' of FIG. 31 is slightly different from the blower housing
shown in
FIG. 20. The purpose of this is to show that various suitable configurations
of the shroud
482 are possible without affecting the scope of the present invention.
As shown in FIG. 20, the shroud 482 is provided with an opening 494 which
surrounds the intake port 444 (FIG. 25). An intake isolator 369 (FIG. 22)
having an
air/fuel passageway 496 (FIGS. 29 and 30) extending therethrough is provided.
The intake
isolator 369 is mounted to the engine housing 330 so that the air/fuel
passageway 496 is
aligned with the intake port 444. The intake isolator 496 is positioned within
the opening
494 of the shroud 482 to substantially ensure that cooling air passing between
the engine
housing 330 and the shroud 482 cannot escape through the opening 494 in the
shroud 482.
Preferably, the intake isolator 369 includes an integrally formed back wall
498 and a side
wall 500 (FIG. 22) to accomplish this feature.
To further reduce manufacturing costs, the crankcase 420, the cylinder 422 and
the
back plate 438 are cast as a single component. In a preferred embodiment, the
engine
housing 330 further includes at least one fin 502 integrally formed thereto
(FIG. 28). The
fin 502 extends from the back plate 438 and beneath the crankcase 420 for
stability and
cooling purposes.
Although the shroud 482 may be of many different designs consistent with the
principles of the present invention, the shroud 482 is designed to hold the
fuel tank 412.
As best shown in FIG. 31, the shroud 482 is provided with a pair of opposed
channels 504
(only one is shown). The outwardly extending shoulders 416 (see also FIG. 22)
are
received by the respective channels 504 so that the fuel tank 412 is held by
the shroud 482.
The filler material 418 (see also FIG. 22), preferably a polyethylene, high-
density, closed
cell, high-temperature and gasoline-resistant foam material, is positioned
between each
channel 504 and the respective shoulder 416 to provide a tight fit between the
shroud 482
and the fuel tank 412. The fuel line 414 (FIG. 22) includes a fuel filter 506
attached to the



CA 02368207 2001-07-20
WO 00/43655 PCT/US00/00841
-31-
end of the fuel line 414 disposed within the fuel tank 412. It should be noted
that the extra
line shown in FIG. 22 is a purge line. The fuel filter 506 acts as a weight
such that during
operation of the engine, if the engine is tipped, the weighted fuel line 414
swings to the
bottom of the fuel tank 412 to ensure that fuel is picked up by the fuel line
414.
Another aspect of the present invention concerns the starter assembly 507
shown in
FIG. 33. The blower housing 348 is provided with a hub 508 having an inwardly
facing
extension 510. The hub 508 is adapted to fit over the crankshaft 392 (FIG. 22)
or
crankshaft adapter 338 (FIG. 21). The starter assembly 507 which includes the
pulley 516,
rope 518 and spring 520 is positioned onto the hub 508. A star washer 514 is
placed over
the hub extension 510 so as to dig into the extension material. The star
washer S 14 holds
the starter assembly 507 in place with respect to the blower housing 348. This
arrangement eliminates the need for separate mounting bosses and fasteners
typically
needed to hold the starter assembly in place. Such mounting bosses and
fasteners
generally block the cooling air flow by a fan.
1 S FIGS. 34-38 show various views of the pulley S 16. The spring 520 (FIG.
33) is
positioned on one side 522 of the pulley 516 having an appropriately shaped
annular
recess 524. The opposite side 526 of the pulley 516 includes a plurality of
spokes 528 for
engagement with a flywheel such as flywheel 336 shown in FIG. 21. The rope 518
includes a knot 530 on one end thereof which is held in a chamber 532 formed
in a hub
534 of the pulley 516 beneath the pulley rope portion 536. The rope S 18
extends through
a hole 538 in the pulley rope portion 536 and is wrapped around the pulley
516. The other
end of the rope S 18 is attached to a starter handle 540 (FIG. 20).
The foregoing description of the present invention has been presented for
purposes
of illustration and description. Furthermore, the description is not intended
to limit the
invention in the form disclosed herein. Consequently, variations and
modifications
commensurate with the above teachings in skill or knowledge of the relevant
art, are
within the scope of the present invention. The embodiments described herein
are further
intended to explain the best modes known for practicing the invention and to
enable others
skilled in the art to utilize the invention as such, or other embodiments and
with various
modifications required by the particular applications or uses of the present
invention. It is
intended that the appended claims are to be construed to include alternative
embodiments
to the extent permitted by the prior art.
Various features of the invention are set forth in the following claims.

Representative Drawing